Summary. – The Big Bend slider, Trachemys gaigeae (Family Emydidae), is a medium-sized freshwater turtle (carapace length to 308 mm) that is limited to riverine areas of the desert southwestern United States and northern Mexico. Two allopatric subspecies are currently recognized, T. g. gaigeae and T. g. hartwegi, which might represent distinct species. Degradation and fragmentation of riverine habitat is likely the most significant threat to T. gaigeae in both the United States and Mexico. Overcollecting for the pet trade or as food and hybridization with introduced Trachemys scripta are also of concern, although more information is needed. Commercial collection is prohibited in the United States but otherwise this slider receives little protection, except where it occurs on public lands. The species uses reservoirs and artificial ponds in New Mexico, suggesting some adaptability to human-modified environments. The status and ecology of this species in the United States has been little studied until recently and even less is known about populations in Mexico.

Distribution. – Mexico, USA. Occurs in the Rio Grande (= Río Bravo del Norte) drainage from south-central New Mexico downstream to western Texas and northwestern Coahuila, the Río Conchos in Mexico from southern Chihuahua downstream to the confluence with the Rio Grande, and the Río Nazas closed basin of Durango and Coahuila, Mexico.

Distribution of Trachemys gaigeae in the southwestern USA (New Mexico and Texas) and northeastern Mexico. Trachemys g. gaigeae is the disjunct northern distribution, T. g. hartwegi the disjunct southern range. Red points = museum and literature occurrence records based on Iverson (1992) plus more recent and authors’ data; green shading = projected distribution based on GIS-defined hydrologic unit compartments (HUCs) constructed around verified localities and then adding HUCs that connect known point localities in the same watershed or physiographic region, and similar habitats and elevations as verified HUCs (Buhlmann et al., in press), and adjusted based on authors’ data.